Global Sea Level Rise Research Articles

Recent Acceleration of Wetland Accretion and Carbon Accumulation Along the U.S. East Coast

AbstractThe long‐term stability of coastal wetlands is determined by interactions among sea level, plant primary production, sediment supply, and wetland vertical accretion. Human activities in watersheds have significantly altered sediment delivery from the landscape to the coastal ocean, with declines along much of the U.S. East Coast. Tidal wetlands in coastal systems with low sediment supply may have limited ability to keep pace with accelerating rates of sea‐level rise (SLR). Here, we show that rates of vertical accretion and carbon accumulation in nine tidal wetland systems along the U.S. East Coast from Maine to Georgia can be explained by differences in the rate of relative SLR (RSLR), the concentration of suspended sediments in the rivers draining to the coast, and temperature in the coastal region. Further, we show that rates of vertical accretion have accelerated over the past century by between 0.010 and 0.083 mm yr−2, at roughly the same pace as the acceleration of global SLR. We estimate that rates of carbon sequestration in these wetland soils have accelerated (more than doubling at several sites) along with accelerating accretion. Wetland accretion and carbon accumulation have accelerated more rapidly in coastal systems with greater relative RSLR, higher watershed sediment availability, and lower temperatures. These findings suggest that the biogeomorphic feedback processes that control accretion and carbon accumulation in these tidal wetlands have responded to accelerating RSLR, and that changes to RSLR, watershed sediment supply, and temperature interact to determine wetland vulnerability across broad geographic scales.

Integrated effects of bioturbation, warming and sea-level rise on mobility of sulfide and metalloids in sediment porewater of mangrove wetlands

Global warming and sea-level rise exert profound impacts on coastal mangrove ecosystems, where widespread benthic crabs change sediment properties and regulate material cycles. How crab bioturbation perturbs the mobilities of bioavailable arsenic (As), antimony (Sb) and sulfide in sediment-water systems and their variability in response to temperature and sea-level rise is still unknown. By combining field monitoring and laboratory experiments, we found that As was mobilized under sulfidic conditions while Sb was mobilized under oxic conditions in mangrove sediments. Crab burrowing greatly enhanced oxidizing conditions, resulting in enhanced Sb mobilization and release but As sequestration by iron/manganese oxides. In control experiments with non-bioturbation, the more sulfidic conditions triggered the contrasting situation of As remobilization and release but Sb precipitation and burial. Moreover, the bioturbated sediments were highly heterogeneous for spatial distributions of labile sulfide, As and Sb as presented by 2-D high-resolution imaging and Moran's Index (patchy at the <1 cm scale). Warming stimulated stronger burrowing activities, which led to more oxic conditions and further Sb mobilization and As sequestration, whilst sea-level rise did the opposite via suppressing crab burrowing activity. This work highlights that global climate changes have the potential to significantly alter element cycles in coastal mangrove wetlands by regulating benthic bioturbation and redox chemistry.

Weichselian Glaciation of the Faroe Islands

This paper presents a new complete field mapping of glacial landscapes, landforms and sediments in the Faroe Islands, supplemented by observations from bathymetric maps of the Faroe Shelf. In addition, previous investigations of Quaternary and espe-cially the Weichselian glaciation of the archipelago are reviewed. New cosmogenic nuclide exposure ages indicate that the last extensive glaciation of the Faroe Islands occurred during the Late Weichselian, most likely during the Last Glacial Maximum (LGM; c. 26.5–19.0 cal. ka BP), although a Younger Dryas (c. 12.9–11.7 cal. ka BP) age cannot be entirely excluded. Geomorphological mapping provides a background for reconstructing the extent and type of the glaciation of the Faroe Islands. The reconstructed Weichselian glaciation appears to have had the character of an exten-sive valley glaciation, with several marine glacier termini. The present glaciation of southern Spitsbergen, Svalbard, represents a modern analogue of the reconstructed Weichselian glaciation in the Faroe Islands. The lack of raised coastal features in the Faroe Islands, also at protected sites, suggests that postglacial isostatic uplift was smaller than post-LGM eustatic sea level rise. Numerical glacier reconstructions carried out for different extents of the last extensive Faroese glaciation suggest that such limited postglacial isostatic crustal uplift requires that the Faroe Shelf was not extensively glaciated during the Late Weichselian, but it doubtless was so during at least one of the previous Quaternary glaciations.

Future sea-level projections with a coupled atmosphere-ocean-ice-sheet model

Climate-forced, offline ice-sheet model simulations have been used extensively in assessing how much ice-sheets can contribute to future global sea-level rise. Typically, these model projections do not account for the two-way interactions between ice-sheets and climate. To quantify the impact of ice-ocean-atmosphere feedbacks, here we conduct greenhouse warming simulations with a coupled global climate-ice-sheet model of intermediate complexity. Following the Shared Socioeconomic Pathway (SSP) 1-1.9, 2-4.5, 5-8.5 emission scenarios, the model simulations ice-sheet contributions to global sea-level rise by 2150 of 0.2 ± 0.01, 0.5 ± 0.01 and 1.4 ± 0.1 m, respectively. Antarctic ocean-ice-sheet-ice-shelf interactions enhance future subsurface basal melting, while freshwater-induced atmospheric cooling reduces surface melting and iceberg calving. The combined effect is likely to decelerate global sea-level rise contributions from Antarctica relative to the uncoupled climate-forced ice-sheet model configuration. Our results demonstrate that estimates of future sea-level rise fundamentally depend on the complex interactions between ice-sheets, icebergs, ocean and the atmosphere.

Spatial–Temporal Evolution Monitoring and Ecological Risk Assessment of Coastal Wetlands on Hainan Island, China

Coastal wetlands are located at the intersection of land and sea and provide extremely important ecological services. The coastal wetlands of estuarine harbors are representative parts of the coastal wetlands. Changes that occur in estuarine harbor wetlands are microcosms of the changes occurring in the coastal wetlands more generally. The coastal wetlands of Hainan Island, China, are coastal wetlands typical of tropical islands and are extremely sensitive to climate change. In the context of global sea level rise, studying the characteristics of spatial and temporal distribution of coastal wetlands on Hainan Island, as well as changes in their vulnerability, could provide scientific and technological support to address the adverse effects of climate change. Using nine typical estuarine harbor wetlands as target areas, this study systematically studies the spatial–temporal evolution of coastal wetlands on Hainan Island from 1990 to 2020. The results suggest the following: (1) The total area of coastal wetlands has remained relatively stable, but the area of artificial wetlands, especially aquaculture ponds, has increased significantly. There is a clear spatial variability in the changes in mangrove wetlands, with a clear increase in the area of areas with a high degree of protection, such as Dongzhai Harbor (DZG). The area of the areas with a high intensity of human activity has been significantly reduced, such as Bamen Bay (BMG). (2) The overall ecological risk of coastal wetlands is low, with the average wetland risk index (WRI) of all harbors being below 0.15. The higher the degree of protection, the lower the ecological risk of the area, such as DZG. Human activities are the main factor causing increased ecological risk in wetlands. (3) Climate-change-induced sea level rise and the intensification of human activities are the main determinants of future trends in the spatial distribution of coastal wetlands and wetland ecosystem stability. The results of this study provide guidance on the conservation and restoration of coastal wetlands.

Transgressive rocky coasts in the geological record: Insights from Miocene granitic rocky shorelines and modern examples

Rocky shorelines are commonly punctuated, with alternating high relief cliffs and incised embayments which host “pocket beaches”. While multiple cases of ancient rocky shorelines associated with low relief ravinement surfaces have been documented in the geological record, deposits formed in pocket beaches and joint-cut coves are more rarely described. This poses the question “are high relief rocky coastlines and their associated deposits not preserved or have they been previously overlooked? Here we document exhumed examples of ancient granitic rocky shoreline systems of diverse morphologies from the Early Miocene of northern Austria, and compare them with modern systems in UK, Corsica, Spain and Norway. The preserved ancient examples offer a good opportunity to characterize these sedimentary systems, provide diagnostic criteria for their recognition and discuss the main controls on their occurrence and preservation in the rock record.From their stratigraphic and sedimentological analysis, and its comparison with modern examples, we interpret that these rocky shorelines form and get preserved during rapid rates of combined tectonic and eustatic sea-level rise, along lithological, structural and weathered “weakness” zones affected by normal low wave energy conditions interrupted by storms. These results provide a mechanism for predicting their potential occurrence and distribution during transgression of rocky coasts, with implications for exploration around structural highs and coastal management.

Epistemic uncertainty in the kinematics of global mean sea-level rise since 1993 and its dire consequences

Recent studies reported an ambiguous global sea level acceleration during the satellite altimetry (SA) era (1993–2017). New SA data created an opportunity to resolve this issue. In this study, two competing kinematic models to represent global mean sea level anomalies are compared. The first model consists of an initial velocity and uniform acceleration. The second model replaces the initial velocity and acceleration with a trend and a representation of a long periodic lunar subharmonic of period 55.8 y, which is determined to be statistically significant at globally distributed tide gauge records. The models also include parameters for the periodic effects of lunisolar origin with periods 18.6 y and 11.1 y annual, and biannual variations in 10-day average of globally SA measurements during 1993–2022. Generalized least squares solutions yielded updated statistically significant estimates for all the model parameters and their statistics for both models. However, the outcome failed to resolve the ambiguity of uniform acceleration in global mean sea level confounded with the long periodic lunar subharmonic of period 55.8 y during this period. This epistemic uncertainty will have a dire impact on climate change risk assessments as demonstrated through the prospective comparison of both kinematic models.

One-degree resolution mascon solution over Antarctic derived from GRACE Level-2 data

The mass loss of the Antarctic Ice Sheet (AIS) is an important contributor to global sea-level rise in response to the warming ocean and atmospheric temperatures as well as the changes in current systems and precipitation patterns. In this study, a regional mascon method is developed to squeeze more mass change signals, in which the pseudo-observations of the geopotential are generated from the unfiltered GRACE Level-2 data whereas the regularization matrix is constructed with the prior information derived from filtered GRACE Level-2 data. A series of mascon solutions with 1°×1° equal-area resolution over AIS is derived from the updated Tongji-Grace2018 model spanning April 2002 to December 2016. Compared to the filtering results from P4M6 decorrelation and 100 km Gaussian filtering, our mascon solutions can effectively suppress the strips, improve the spatial resolution over AIS, and get a stronger signal with an improvement of 116.86% in the Antarctic Peninsula Ice Sheet (APIS), and more coincide with the features of glaciers and ice streams, such as the most striking ice mass loss in Totten, Getz, Thwaites and Pine Island, and the ice mass gain in Kamb Ice Stream. During the period from 2002 to 2016, the mass change rates from our mascon solution are −103.6 ± 5.6 Gt/yr, 63.0 ± 4.3 Gt/yr, −143.3 ± 4.9 Gt/yr and −23.29 ± 1.2 Gt/yr in AIS, East AIS, West AIS, and APIS, respectively. The mass change signals at the basin scale are with even more distinguishing features, with the highest mass gain rates of 18.03 ± 1.88 Gt/yr and 14.55 ± 0.60 Gt/yr at Basin 7 and Basin 18, and the highest mass loss rates of −58.57 ± 2.48 Gt/yr and −44.12 ± 2.27 Gt/yr at Basin 21 and Basin 22. Relative to the cumulated surface mass balance from the regional atmospheric climate model, the correlation coefficients of our mascon solutions are 0.91, 0.94, and 0.96 in East AIS, West AIS, and APIS.

Breakup of Pangea and the Cretaceous Revolution

AbstractA 250 Ma, Pangea had just reached an equatorial position of dynamic equilibrium, after a 60° northward migration due to True Polar Wandering. It then began oscillating about itself for the next 150 Myr. The resulting extensional stresses triggered three successive phases of breakup, controlled by the mechanical resistance of a crescent of thick lithosphere, surrounding the Tethyan realm, which had adjusted the supercontinent to its hemispheric shape. The fracturing of the crescent was produced in three successive generations, each new generation corresponding to Coulomb fractures, conjugates of the preceding set. Flood basalts were associated with these deep fractures within the thick lithosphere crescent. We consider unlikely that this highly ordered pattern of fracturing was determined by the locations of the impacts of successive plumes. Between 260 and 180 Ma, thermal isolation was maximal and the asthenosphere of Pangea was about 150°C warmer than below Panthalassa. From 180 to 100 Ma, the breakup elongated Pangea by about 3,000 km in a north‐northwest–south‐southeast direction, producing gaps in the subduction girdle. Lateral mixing began, leading to a continuous rise in global sea level and progressive return to a globally homogeneous upper mantle with sea‐level at its maximum 100 Ma. This Cretaceous Revolution marked the end of the Pangea tectonics, radically different from our present plate tectonics. Neither post‐Cretaceous plate kinematic inferences, nor mantle dynamic and associated planetary cooling inferences are extendable to Pangea times.

Rapid Prediction Model for Urban Floods Based on a Light Gradient Boosting Machine Approach and Hydrological–Hydraulic Model

Global climate change and sea level rise have led to increased losses from flooding. Accurate prediction of floods is essential to mitigating flood losses in coastal cities. Physically based models cannot satisfy the demand for real-time prediction for urban flooding due to their computational complexity. In this study, we proposed a hybrid modeling approach for rapid prediction of urban floods, coupling the physically based model with the light gradient boosting machine (LightGBM) model. A hydrological–hydraulic model was used to provide sufficient data for the LightGBM model based on the personal computer storm water management model (PCSWMM). The variables related to rainfall, tide level, and the location of flood points were used as the input for the LightGBM model. To improve the prediction accuracy, the hyperparameters of the LightGBM model are optimized by grid search algorithm and K-fold cross-validation. Taking Haidian Island, Hainan Province, China as a case study, the optimum values of the learning rate, number of estimators, and number of leaves of the LightGBM model are 0.11, 450, and 12, respectively. The Nash-Sutcliffe efficiency coefficient (NSE) of the LightGBM model on the test set is 0.9896, indicating that the LightGBM model has reliable predictions and outperforms random forest (RF), extreme gradient boosting (XGBoost), and k-nearest neighbor (KNN). From the LightGBM model, the variables related to tide level were analyzed as the dominant variables for predicting the inundation depth based on the Gini index in the study area. The proposed LightGBM model provides a scientific reference for flood control in coastal cities considering its superior performance and computational efficiency.

Shoreline Dynamics Assessment of Moheshkhali Island of Bangladesh using Integrated GIS-DSAS Techniques

Coastal areas of Bangladesh are more susceptible to the adverse effects of climate change due to their geographic location and geological condition. The coastal zones and offshore islands of the country have indisputably experienced the combined consequences of global temperature and sea level rise. Aiming to study and understand shoreline dynamics and shoreline change, medium resolution (30m) satellite imagery over 30 (1990-2020) years was being executed. The Digital Shoreline Analysis System (DSAS) in the GIS platform was used in conjunction with other geospatial techniques to ascertain shoreline dynamics in multiple satellite images taken over this period, and afterward, the spatial outcomes were validated through a detailed field investigation. The study demarcated that the shoreline of Moheshkhali is subjected to severe erosion and accretion and has undergone significant morphological changes. On the basis of average shoreline change rates, the island's shoreline is divided into 6 accretion zones and 4 erosion zones, with accretion being the dominant process. Accretion occurs in the south and south-western parts of the island, particularly those near the sea heads, which have experienced significant accretion at a rate of more than 86 m/yr and the consequent westward and south-east migration of the shore due to the active deposition along the coast. Besides, minor alterations were observed in the north and north-eastern part of the island. The study also evident that climate change, windy storms, variability in coast material, intermittent wave and air action, longshore transport, and anthropogenic activities are prime factors that contribute to the highly dynamic nature of the shorelines of Moheshkhali island. Therefore, this study demonstrates the benefit of using an integrated GIS-DSAS tool to investigate spatiotemporal shoreline change, and it might be valuable in land-use planning and coastal erosion mitigation on Moheskhali Island.&#x0D; The Dhaka University Journal of Earth and Environmental Sciences, Vol. 11(1), 2022, P 1-13&#x0D;

Impacts of river discharge, coastal geomorphology, and regional sea level rise on tidal dynamics in Pearl River Estuary

IntroductionRecently, accelerated sea-level rise (SLR) has raised major concerns on estuarine management and restoration because it modifies estuarine hydrodynamics, such as tidal inundation extent and amplitude, tidal current asymmetry, flood frequency, etc. Understanding underlying processes which regulate estuarine tidal dynamics is critical for mitigating potential impacts on the coastal population and development.MethodsWe selected the Pearl River Estuary (PRE), an estuary with a higher regional SLR compared to the global SLR as the study area. To identify the effects of regional SLR on tidal dynamics, we analyzed long-term records of four tidal variables from 19 gauge stations between 1952 and 2020, including annual highest tidal levels (AHTLs), annual lowest tidal levels (ALTLs), annual mean tidal ranges (AMTRs), and annual mean tidal levels (AMTLs).ResultsResults suggested that variability in tidal variables was site-specific. The AMTRs decreased gradually from offshore regions to the upper reaches of rivers with a maximum at the mouth of the estuary. In contrast, the magnitudes of the AHTLs, AMTLs, and ALTLs decreased when approaching the coastline. Distance to the coastline had the highest correlations with the AHTLs, ALTLs, and AMTLs, followed by river width and river depth. The local SLR was responsible for the temporal variability in AHTLs, ALTLs, and AMTLs at the estuarine mouth with correlation coefficients from 0.43 to 0.85 (P &amp;lt; 0.001) but showed low correlations with these three tidal variables at the upper reaches of rivers (P &amp;gt; 0.001). Instead, the tidal variables were highly correlated with river discharge at the upper reaches of rivers, especially for the AHTLs (correlation coefficient = 0.83, P &amp;lt; 0.0001).ConclusionsOur study demonstrated that the tidal dynamics demonstrate significant spatial-temporal variability. Geomorphology, river discharge, and sea levels have jointly affected estuarine hydrodynamics.

Study of the spatial and temporal distributions of tidal flat surface sediment based on multitemporal remote sensing

IntroductionThe ecological environment of tidal flats often changes due to tidal erosion and sedimentation. The distribution of tidal flat surface sediment is a natural reflection of the changes in the external dynamic environment, the spatial and temporal distribution pattern is of great significance.MethodsIn this study, the output structure of traditional convolutional neural network is combined with BP neural network. Meanwhile, four phases of Sentinel-2 multispectral images were collected and combined with field data from the Doulonggang tidal flat in Jiangsu Province, China, to construct the sediment composition inversion model.ResultsThe inversion accuracy was higher than 80% compared with the measured results. According to the inversion result, from 2017 to 2022, the surface sediment particle size of the tidal flat in Jiangsu varied seasonally and was coarse in summer and fine in winter. Additionally, the sediment composition tended to coarsen, showing an interannual change trend of increasing sand content and decreasing clay and silt contents.DiscussionThe above change of the sedimentary environment of the tidal flat may be caused by the decrease of fine grained sediment deposition, the introduction of exotic vegetation, the global sea level rise and the influence of human activities.

Retreat and stabilization of a marine-based ice margin along a high arctic fjord-cross-shelf trough system

Multibeam bathymetric and seismostratigraphic data collected in the Clyde fjord-cross-shelf trough system (eastern Baffin Island, Canadian Arctic Archipelago) display glacial landforms and depositional assemblages that enable the identification of the maximal extent of the Laurentide Ice Sheet (LIS) margin and delineating the patterns and controls on its subsequent retreat. Additionally, 10 new sediment cores – from which seven radiocarbon ages were acquired – allow the recognition of depositional processes. Results show that, during the Last Glacial Maximum, the LIS margin extended almost to the edge of the continental shelf. Early deglaciation of the trough was marked by an initial ice-shelf collapse and rapid retreat of the ice stream, as evidenced by the absence of ice marginal landforms and the presence of extensive iceberg ploughmarks across a large portion of the outer trough. It was followed by a slow retreat and successive stabilizations of the ice margin that led to the deposition of recessional moraines and grounding-zone wedges (GZWs). Deglaciation of the fjord in the early Holocene occurred in an episodic style, whereby rapid retreat was punctuated by relatively long standstills that enabled major moraine formation. Long-term stabilizations of the ice margin in the Clyde fjord-cross-shelf trough system are interpreted to coincide with major climatic cooling events, such as the Younger Dryas and early Holocene cold reversals. Ages derived from sediment cores and previous work suggest that higher retreat rates correspond with periods of significant global sea level rise, suggesting that oceanic forcing exerted a minor control on the deglaciation. GZWs and large moraine ridges are observed at pinning points in the trough and fjord, indicating that the location of ice margin stabilizations was influenced by topography. The reconstruction of the deglaciation of the Clyde fjord-cross-shelf trough system allows us to refine deglacial models for similar systems of northeastern Baffin Island, in particular beyond the coast and along the steeper section of the fjord where chronological gaps remained.

Inter-decadal climate variability induces differential ice response along Pacific-facing West Antarctica

West Antarctica has experienced dramatic ice losses contributing to global sea-level rise in recent decades, particularly from Pine Island and Thwaites glaciers. Although these ice losses manifest an ongoing Marine Ice Sheet Instability, projections of their future rate are confounded by limited observations along West Antarctica’s coastal perimeter with respect to how the pace of retreat can be modulated by variations in climate forcing. Here, we derive a comprehensive, 12-year record of glacier retreat around West Antarctica’s Pacific-facing margin and compare this dataset to contemporaneous estimates of ice flow, mass loss, the state of the Southern Ocean and the atmosphere. Between 2003 and 2015, rates of glacier retreat and acceleration were extensive along the Bellingshausen Sea coastline, but slowed along the Amundsen Sea. We attribute this to an interdecadal suppression of westerly winds in the Amundsen Sea, which reduced warm water inflow to the Amundsen Sea Embayment. Our results provide direct observations that the pace, magnitude and extent of ice destabilization around West Antarctica vary by location, with the Amundsen Sea response most sensitive to interdecadal atmosphere-ocean variability. Thus, model projections accounting for regionally resolved ice-ocean-atmosphere interactions will be important for predicting accurately the short-term evolution of the Antarctic Ice Sheet.

InSAR time-series analysis and susceptibility mapping for land subsidence in Semarang, Indonesia using convolutional neural network and support vector regression

Global sea-level rise due to climate change is a critical problem for coastal cities. One of the coastal cities in Indonesia, Semarang, is in danger of being submerged by seawater due to flooding, which is exacerbated by land subsidence. Time-series analysis based on persistent scatterer (PS) interferometry usually suffers from sparse measurement points (MP), and thus does not completely cover the study area with low coherence. In this study, we utilized improved combined scatterers interferometry with optimized point scatterers (ICOPS) to increase the MP density. We also compared the optimization of the ICOPS method based on support vector regression (SVR) with convolutional neural network (CNN) algorithms. The ICOPS-CNN showed better model performance and MP density, and was less time-consuming. Further land subsidence analysis was conducted in Semarang using susceptibility mapping. The land subsidence susceptibility map from the standalone deep learning (DL) algorithm (CNN = 0.833) outperformed the standalone machine learning (ML) algorithm (SVR = 0.820). The hybrid DL algorithm with grey wolf optimizer (GWO) (CNN-GWO = 0.907) exhibited the highest accuracy, followed by the hybrid ML algorithm (SVR-GWO = 0.843). The accuracy was consistent with the comparison between the susceptibility maps and the ICOPS measurements, resulting in a susceptibility map based on CNN-GWO with the highest accuracy (0.889). Land subsidence monitoring using ICOPS based on CNN and susceptibility mapping based on a hybrid DL algorithm (CNN-GWO) can be used by local governments to improve urban development planning in Semarang and its surrounding areas.

Shoreline change due to global climate change and human activity at the Shandong Peninsula from 2007 to 2020

In this study, how shoreline change responses to global climate change and human activity at the Shandong Peninsula was quantified by analyzing shoreline locations, inshore erosion/accretion rates, and sandy beach profiles for 2007–2020. During the study period, the total shoreline length decreased from 3345.55 km to 3310.18 km, whereas the natural shoreline decreased by 25.41%. As a dominant shore type, the artificial shoreline increased by 827.89 km. Human activities, such as land reclamation and harbor construction, have caused continuous shoreline advance, resulting in a net land increase of 672.40 km2. However, natural shores (e.g., sandy shore) receded at an average annual rate of −1.0 m due to ongoing erosion. The inshore waters of the Shandong Peninsula were largely sedimentary as erosion occurred only at a few hotspots. Therefore, seaward sediment deposition dominated the erosion/accretion trends of the inshore areas of the peninsula. However, global climate change and human activities have exacerbated the erosion caused by sea level rise. Specifically, the climate change caused absolute sea level rise and increasing frequency of extreme weather events, whereas the human activity dominated the transport and supply of sediment in the coastal zone. In the short term, the shoreline of the Shandong Peninsula continues to advance toward the sea due to the growing artificial shoreline. However, this disrupts the balance between sediment supply and marine energies in the coastal zone, and the system then rebalance itself by eroding unprotected natural shores. In the long term, main shoreline evolution trends depend on global climate change and sea level rise which plays a decisive role in shoreline retreat in the Shandong Peninsula.

Coastal switching of dominant depositional processes driven by decreasing rates of Holocene sea-level rise along the macrotidal coast of Gochang, SW Korea

ABSTRACTDecreasing rates of eustatic sea-level rise during the Holocene accompanied the deposition of transgressive coastal deposits worldwide. However, unraveling how transgressive deposition varies in response to different rates of relative sea-level (RSL) rise is limited by the scarcity of long (10+ m) well-dated cores spanning the entire middle to late Holocene record along macrotidal coasts. To investigate the sedimentary response of this macrotidal coast to decreasing rates of RSL rise, we acquired four cores up to 32 m in length and Chirp seismic profiles along the west coast of Korea. Core sediments were analyzed in terms of sedimentary texture, structure, and facies. Nineteen optically stimulated luminescence (OSL) and fourteen 14C accelerated mass spectrometry (AMS) ages constrain the timing of deposition of the sandy sediments. This relatively dense distribution of ages is used to determine how deposition rates changed through time. We also use a compilation of previously published RSL indices for the southwestern Korean coast in order to better constrain RSL changes through time. Results show that the evolution of the Gochang coastline switched from a tide-dominated environment to a wave-dominated environment during the latter stage of transgression as the rate of the sea-level rise decreased. Rugged antecedent topography likely led to the development of tidal currents and the formation of a tide-dominated tidal flat during rapid RSL rise from 10 to 6 ka. As the tidal channels filled with fine-grained sediments from 6 to 1 ka, tidal amplification likely waned leading to a greater role of wave energy in shaping the formation of the sandy open-coast tidal flat. Since 1 ka, wave-dominated environments formed sand-rich tidal beaches and flats. Decreasing changes in rates of the RSL rise resulted in changes in depositional environments from a tide-dominated intertidal flat to an open-coast tidal flat and finally a wave-dominated tidal beach. This study highlights the important role that rates of RSL rise play on not only sedimentation rates in a shelf setting but also playing a role in the switch from a tide-dominated to a wave-dominated setting.

Forcing Mechanisms of the Interannual Sea Level Variability in the Midlatitude South Pacific during 2004–2020

Over the past few decades, the global mean sea level rise and superimposed regional fluctuations of sea level have exerted considerable stress on coastal communities, especially in low-elevation regions such as the Pacific Islands in the western South Pacific Ocean. This made it necessary to have the most comprehensive understanding of the forcing mechanisms that are responsible for the increasing rates of extreme sea level events. In this study, we explore the causes of the observed sea level variability in the midlatitude South Pacific on interannual time scales using observations and atmospheric reanalyses combined with a 1.5 layer reduced-gravity model. We focus on the 2004–2020 period, during which the Argo’s global array allowed us to assess year-to-year changes in steric sea level caused by thermohaline changes in different depth ranges (from the surface down to 2000 m). We find that during the 2015–2016 El Niño and the following 2017–2018 La Niña, large variations in thermosteric sea level occurred due to temperature changes within the 100–500 dbar layer in the midlatitude southwest Pacific. In the western boundary region (from 30°S to 40°S), the variations in halosteric sea level between 100 and 500 dbar were significant and could have partially balanced the corresponding changes in thermosteric sea level. We show that around 35°S, baroclinic Rossby waves forced by the open-ocean wind-stress forcing account for 40 to 75% of the interannual sea level variance between 100°W and 180°, while the influence of remote sea level signals generated near the Chilean coast is limited to the region east of 100°W. The contribution of surface heat fluxes on interannual time scales is also considered and shown to be negligible.

National assessment of extreme sea-level driven inundation under rising sea levels

Episodic inundation from extreme sea-levels (ESLs) will have increasing social and economic impacts in response to relative sea level rise (RSLR). Despite the improved global understanding of ESL frequencies and magnitudes, detailed nationwide inundation maps are unavailable for many countries. This study quantifies New Zealand’s land area exposure to inundation from ESLs and RSLR by: (i) calculating ESL heights for nine annual recurrence intervals (ARI) between 2 and 1,000-years, (ii) converted into space-varying water surface grids, (iii) developing a composite topographical dataset comprised of Airborne Light Detection and Ranging (LIDAR) and bias corrected Shuttle Radar Topography Mission (SRTM), (iv) modifying topographical data to represent mitigation structures, and (v) executing a scalable static model to map land inundation areas for 0.1 m RSLR increments. This modular approach supports continuous integration of new models and data at resolutions appropriate for quantifying inundation hazard and risk trends. In response to 0.1 m–0.4 m RSLR expected in the New Zealand region from 2040 to 2070 under SSP5-8.5 global mean sea level rise scenarios, a rapid cumulative inundation area increase is observed for 10 and 100-year ESL ARIs at national and regional levels. The RSLR time independent maps developed here supports future investigations of ESL inundation hazards and risks for any prescribed RSLR heights or timeframes.